The US is not a democracy, rather a Representative Republic for a Union of States, not much different than the European Union concept, where all 27 included members have common interest on particular and intended issues.
In the case of War, Congress is the only authority that can declare war and where any financing for that war, comes from. On Afghanistan and/or Iraq or many probable covert actions (Pakistan) were agreed to and financed by Congress, at the request of the President and then financed. Many European Countries, including the UK were drawn into Afghanistan under the agreements between NATO Nations, declaring an act of war (9/11) is an act against all NATO members. Since all treaties are entered into by the various societies representatives, any form of Government, the Democracy angle would be invalid for entering that war. To make clear, NATO, was NOT obligated to the Iraq War and was by choice of those involved, in the US our Congress. I won't speak for the various Parliaments, but strongly suggest they may have had less choice than you might think.